CN109347087A - Optimization of Doubly-fed Wind Turbine Based on Adjustment of Pole Pairs and Transmission Ratio - Google Patents

Abstract

The present invention relates to the Double-feed wind power set optimization design methods being applied in AC and DC power grid, belong to technical field of wind power generation.This method optimizes the Double-feed wind power unit for including gear-box, current transformer and double-fed generator (DFIG) using the method for adjusting tooth roller box transmission ratio and power generator electrode logarithm；First using after optimization and the ratio λ of optimization front gear box transmission ratio is as parameter, the cost of gear-box, current transformer and double-fed generator before and after building optimization；To ask Double-feed wind power unit after optimization to reduce cost Δ C_s；Finally seek Wind turbines optimal design parameter: according to Δ C_sFormula draws Δ C_s- λ curve acquires Δ C_sMaximum value and λ optimal value, thus to obtain optimization rear gear box transmission ratio and DFIG number of pole-pairs.The present invention can effectively reduce gear box ratio and system cost.

Description

Optimization of Doubly-fed Wind Turbine Based on Adjustment of Pole Pairs and Transmission Ratio

technical field

The invention relates to a system optimization design method, in particular to an optimization design method of a doubly-fed wind generator set applied to AC and DC power grids, and belongs to the technical field of wind power generation.

Background technique

Doubly-fed wind power systems are widely used in AC and DC grid-connected wind farms, and are mainly composed of wind turbines, gearboxes, doubly-fed wind generators (DFIG), and converter systems. The wind turbine runs at a low speed, and the traditional DFIG is a high-speed, small-volume generator, so a high-speed ratio gearbox is usually used to increase the lower wind turbine speed to a high-speed rotor speed. The cost and loss of gearbox and DFIG are proportional to and inversely proportional to the transmission ratio of the gearbox, respectively: the higher the transmission ratio of the gearbox, the smaller the volume and cost of the DFIG, but the larger the volume and cost of the gearbox. About 65% of the system loss of the double-fed wind power generation system comes from the gearbox every year. The larger the gear ratio of the gearbox, the higher the loss and failure rate of the system, and the worse the reliability of the system. Therefore, it is necessary to study the optimal design scheme of gearbox and DFIG, in order to reduce the overall cost and loss of DFIG, and improve the reliability of system operation.

In order to directly connect the output power of the doubly-fed wind turbine to the DC grid DFIG, the applicant's invention patent ZL201310079881.6 discloses a DFIG converter topology for a flexible DC transmission system . At the same time, the invention patent 107273647A disclosed by the applicant discloses a double-fed method for the topology structure of the DC double-fed wind power generation system in the patent ZL201310079881.6 by using the method of adjusting the gear box transmission ratio and the generator current when the number of pole pairs of the generator is unchanged. However, adjusting the number of generator pole pairs can effectively reduce the gearbox transmission ratio and system cost, so the system optimization design must be solved.

SUMMARY OF THE INVENTION

The main purpose of the present invention is: aiming at the deficiencies and blanks of the prior art, to propose a scheme for optimizing the design of the doubly-fed wind turbine by selecting the optimal gearbox transmission ratio and the number of pole pairs of the doubly-fed wind turbine , in order to achieve the purpose of reducing the cost of the double-fed wind turbine and improving the reliability of the system.

In order to achieve the above purpose, the present invention adopts an optimal design method for a doubly-fed wind turbine by adjusting the transmission ratio of the gearbox and the number of pole pairs of the generator. The optimized design of the doubly-fed wind turbine with the topology of the fed wind power generation system is carried out. The DC converter includes a stator-side converter and a rotor-side converter, and the traditional doubly-fed power generation system topology structure of the AC transmission includes a wind turbine, a gearbox, a doubly-fed wind turbine, a traditional converter, The AC bus, the DC converter and the traditional converter are collectively referred to as a converter system, the doubly-fed wind turbine includes the gearbox, the doubly-fed wind turbine and the converter system, It is characterized in that: it comprises the following steps:

Step 1: Calculate the total cost reduction ΔC _s of the doubly-fed wind turbine after optimization:

In the formula, ΔC _d and ΔC _g are respectively the reduced cost of the DFIG wind turbine and the increased cost of the gearbox after optimization; C _d,N , C _g,N are the DFIG before optimization, respectively The cost of the wind turbine and the gearbox; k ₁ , k ₂ , and k ₃ are respectively the fitting coefficients of the cost curve of the gearbox, and the cost of the gearboxes with different transmission ratios in industrial applications is calculated by using the curve fitting method. The fitting coefficient is obtained by curve fitting; λ is the ratio of the transmission ratio M of the gearbox after optimization to the transmission ratio N of the gearbox before optimization, which can be expressed as

The number of pole pairs of the generator after optimization is

In the formula, n _p,N , n _p,M are the number of pole pairs before and after optimization, respectively

Step 2, find the optimal design parameters of the doubly-fed wind turbine, which specifically includes the following steps:

1) Taking λ as the abscissa and the reduced cost ΔC _s of the doubly-fed wind turbine as the ordinate, draw a curve according to formula (1), and obtain the maximum value ΔC _smax of the optimized cost reduction of the doubly-fed wind turbine, and The corresponding optimal gearbox ratio λ _opt ;

2) Substitute λ=λ _opt into formula (2) to obtain the optimized transmission ratio M=λ _opt N of the gearbox;

3) Substitute λ=λ _opt into Equation (3) to obtain the number of pole pairs n _pM =n _pN /λ _opt of the doubly-fed wind turbine after optimization.

The beneficial effects of the invention are: with the reduction of the transmission ratio of the gear box, the volume of the gear box is reduced, the cost is reduced, and the failure rate is reduced, so that the cost of the whole machine system is reduced, and the reliability of the system operation is improved.

Description of drawings

FIG. 1 is a schematic diagram of the topology structure of the DC double-fed wind power generation system adopted in the present invention.

FIG. 2 is a schematic diagram of a topology structure of an AC traditional doubly-fed wind power generation system adopted in the present invention.

Figure 3 is a graph showing the relationship between the change in system cost and the ratio λ of the gearbox transmission ratio after optimization.

Among them, 1-wind turbine; 2-gearbox; 3-double-fed wind turbine; 31-stator of double-fed wind turbine; 32-rotor of double-fed wind turbine; 4-DC converter; 41-stator side converter; 42-rotor side converter; 5-DC bus; 6-traditional converter; 7-AC bus.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings.

As shown in FIG. 1 , the DC double-fed wind power generation system adopted in the present invention includes a wind turbine 1, a gear box 2, a double-fed wind turbine 3, a DC converter 4, and a DC bus 5; the DC converter 4 includes The stator-side converter 41 and the rotor-side converter 42; one end of the gearbox 2 is connected to the wind turbine 1, and the other end is connected to the doubly-fed wind turbine rotor 32; one end of the stator-side converter 41 is connected to the doubly-fed wind turbine generator The machine stator 31 is connected, and the other end is connected with the rotor-side converter 42 and the DC bus 5 respectively; the other end of the rotor-side converter 42 is connected with the doubly-fed wind turbine rotor 32 . The gearbox 2, the DFIG 3 and the DC converter 4 are collectively referred to as a DC DFIG.

As shown in FIG. 2, the AC doubly-fed wind power generation system adopted in the present invention includes a wind turbine 1, a gearbox 2, a doubly-fed wind turbine 3, a traditional converter 6, and an AC bus 7; the traditional converter 6 is Two back-to-back converters; one end of the gearbox 2 is connected to the wind turbine 1, and the other end is connected to the doubly-fed wind turbine rotor 32; one end of the traditional converter 6 is connected to the doubly-fed wind turbine rotor 32, and the other end It is connected with the AC bus bar 7; the AC bus bar 7 is connected with the stator 31 of the doubly-fed wind power generator. The gearbox 2 , the doubly-fed wind generator 3 and the traditional converter 6 are collectively referred to as an AC doubly-fed wind turbine.

The DC doubly-fed wind turbine and the AC doubly-fed wind turbine are collectively referred to as a doubly-fed wind turbine; the DC converter 4 and the traditional converter 6 are collectively referred to as a converter system.

The present invention adopts the optimal design method of the doubly-fed wind turbine generator set by adjusting the gear box transmission ratio and the number of generator pole pairs, and optimizes the design of the doubly-fed wind turbine generator set adopting the topology structure of the AC and DC doubly-fed type wind power generation system, specifically including the following step:

Step 1. Calculate the total cost ΔC _s reduced by the optimized DFIG

Assuming that the power of the wind turbine 1 remains unchanged before and after the optimization, the inductive reactance of the stator 31 and the rotor 32 of the double-fed wind turbine (DFIG) 3 and the mutual inductance between the stator and the rotor remain unchanged, and the stator and rotor currents of the stator 31 remain unchanged. change, let:

In the formula, N and M are the transmission ratios of the gearbox 2 before and after optimization, respectively, and N>M, λ is the ratio of the transmission ratios of the gearbox 2 after optimization and before optimization;

The output power P, torque _Te , stator magnetic flux ψ _s and current of the doubly-fed wind turbine generator 3 are related as follows:

In the formula, ω _m is the rotor speed, ψ _s is the stator magnetic flux, I _sq is the stator active shaft current, and n _p is the number of generator pole pairs.

Before and after the optimization, the power and the current of the stator 31 and the rotor 32 remain unchanged, and the inductive reactance and mutual inductance of the stator and the rotor remain unchanged, so the stator magnetic flux remains unchanged. have to:

P=Nn _p,N ψ _s I _sq ω _w =Mn _p,M ψ _s I _sq ω _w (5)

In the above two formulas, n _p,N , n _p,M are the number of pole pairs before and after optimization, respectively, T _e,N , T _e,M are the torque before and after optimization, respectively, ω _w is the wind turbine Rotating speed.

According to Equation (5) and Equation (2), the optimized pole pair number can be obtained as

Before the optimal design, the cost of the DFIG 3 is C _d,N , the cost of the gearbox 2 is C _g,N , the cost of the converter system is C _c,N , and the total cost of the DFIG is C , N . The cost is C _s,N , then we have

C _s,N =C _d,N +C _g,N +C _c,N (7)

After setting the optimal design, the cost of the DFIG 3 is C _d,M , the cost of the gearbox 2 is C _g,M , the cost of the converter system is C _c,M , and the total cost of the DFIG is C d,M . The cost is C _s,M , then we have

C _s,M =C _d,M +C _g,M +C _c,M (8)

Under the condition of constant transmission power, the cost C _g,M of the gearbox 4 is mainly determined by its speed ratio and torque. With the decrease of λ, it can be estimated as

C _g,M =f(λ)=C _g,N (k ₁ λ+k ₂ λ ² +k ₃ λ ³ ) (9)

In the formula, k ₁ , k ₂ , and k ₃ are the fitting coefficients of the cost curve of the gearbox 4 respectively, which are used to fit the cost curve of the gearbox that changes with λ. The fitting coefficient is obtained by fitting the cost curve of the gear box of the ratio.

The reduced cost ΔC _g of the optimized gearbox can be expressed as

ΔC _g =C _g,N -C _g,M =C _g,N (1-k ₁ λ-k ₂ λ ² -k ₃ λ ³ ) (10)

In the case of the same rotational speed, the cost of the doubly-fed wind turbine 3 is proportional to the torque, so according to equations (2) and (6), the cost of the optimized doubly-fed wind turbine 3 can be estimated as

The added cost ΔC _d of the optimized DFIG can be expressed as

The cost of the converter system is related to its power and current level. Since the output power, the voltage and current of the stator and rotor remain unchanged before and after optimization, the cost of the converter before and after optimization remains unchanged, that is,

C _c,N =C _c,M (13)

The added cost ΔC _c of the optimized converter system is 0, that is,

ΔC _c =C _c,M -C _c,N =0 (14)

After optimization, the total cost reduction ΔC _s of the doubly-fed wind turbine can be expressed as:

ΔC _s =C _s,N -C _s,M =(C _d,N -C _d,M )+(C _g,N -C _g,M )+(C _c,N -C _c,M ) (15 )

Substituting Equation (9), Equation (11) and Equation (13) into Equation (15), the total cost ΔC _s reduced by the optimized doubly-fed wind turbine can be obtained as:

Step 2, seek the optimal design of the double-fed wind turbine, which specifically includes the following steps:

1) As shown in Figure 3, taking λ as the abscissa and the cost as the ordinate, according to formula (10), formula (12) and formula (1), draw the cost reduction ΔC _g -λ curve of gearbox 2, the double-fed The incremental cost ΔC _d -λ curve of the DFIG wind turbine 3, the total cost reduction ΔC _s -λ curve of the DFIG wind turbine system, and the maximum value of ΔC _s ΔC _smax is obtained, that is, the optimal doubly-fed wind turbine. The cost reduction, the corresponding λ is the ratio of the optimal gearbox transmission ratio λ _opt ;

2) According to formula (2), obtain the optimized transmission ratio M=λ _opt N of the gearbox 2;

3) According to formula (3), obtain the optimized number of generator pole pairs n _pM =n _pN /λ _opt .

The present invention will be further described below with an example.

Example:

Taking a doubly-fed wind turbine produced by a company as an example, its main parameters are: P = 3MW, n _p = 3, gearbox transmission ratio N = 80; gearbox cost C _{g, N} = 220,000 euros, DFIG cost C _d,N = 60 thousand euros.

First, by using the curve fitting method to fit the cost curve of gearboxes with different transmission ratios in industrial applications, the values of the fitting coefficients are obtained: k ₁ =0.2, k ₂ =0.35, k ₃ =0.45; according to the formula ( 10), Equation (12) and Equation (1) respectively plot the reduced cost ΔC _g -λ curve of the optimized gearbox, the increased cost ΔC _d -λ curve of the DFIG, and the reduced cost of the DFIG. ΔC _s -λ curve, as shown in Fig. 3. It can be seen from Figure 3 that the reduction cost ΔC _g of the gearbox gradually increases with the decrease of λ; the incremental cost ΔC _d of the DFIG wind turbine gradually increases with the decrease of λ; The reduction cost ΔC _s first increases gradually with the decrease of λ, and then decreases gradually with the decrease of λ, and there is a maximum value. Find the maximum point A in the figure, this point is the optimal point, the corresponding abscissa λ value is the ratio of the optimal gearbox transmission ratio λ _opt = 0.5, and the corresponding ΔC _s ordinate value is the optimized The optimal cost reduction ΔC _smax of the doubly-fed wind turbine is 106,500 euros, which means a saving of 106,500 euros.

Secondly, by substituting λ _opt =0.5 into formula (1), the transmission ratio M=40 of the optimized gearbox can be obtained, and the gearbox can be selected according to the power level.

Finally, by substituting λ _opt =0.5 into equation (2), the number of pole pairs n _p,M =6 of the doubly-fed generator can be obtained, and the doubly-fed wind generator can be selected or designed based on this and other parameters.

Claims (1)

1. a kind of Double-feed wind power set optimization design side using adjusting tooth roller box transmission ratio and power generator electrode logarithm of the present invention Method exchanges traditional double-fed wind-driven power generation system with a kind of based on direct current double-fed wind-driven power generation system topology to using a kind of System topological structure Double-feed wind power unit optimize, the direct current double-fed wind-driven power generation system include wind energy conversion system, Gear-box, double feed wind power generator, DC transformer, DC bus, the DC transformer include stator side current transformer and Rotor-side converter, the double-fed electricity generation system topological structure of the exchange tradition include wind energy conversion system, gear-box, double-feed type wind hair Motor, conventional current transformer, ac bus, the DC transformer and conventional current transformer are referred to as converter system, the double-fed Type Wind turbines include the gear-box, the double feed wind power generator and the converter system, it is characterised in that: including Following steps:

Step 1, after calculation optimization the Double-feed wind power unit totle drilling cost reduction amount Δ C_s:

In formula, Δ C_d、ΔC_gThe reduction cost of the double feed wind power generator and the increase of the gear-box after respectively optimizing Cost；C_d,N、C_g,NThe cost of the double feed wind power generator and the gear-box before respectively optimizing；k₁、k₂、k₃Respectively The fitting coefficient of the gear-box cost curve, by using curve-fitting method to the gear of different drive ratios in industrial application Case carries out cost curve fitting and acquires fitting coefficient；λ is the transmission ratio for optimizing the transmission ratio M and optimization front gear box of rear gear box The ratio between N is represented by

The number of pole-pairs of generator is after optimization

In formula, n_p,N、n_p,MNumber of pole-pairs before respectively optimizing, after optimization

Step 2, the optimal design parameter of the Double-feed wind power unit is sought, specifically includes the following steps:

1) using λ as abscissa, the reduction cost Δ C of Double-feed wind power unit_sFor ordinate, curve is drawn according to formula (1), is acquired The Double-feed wind power unit reduces the maximum value Δ C of cost after optimization_smaxAnd corresponding optimal gear box ratio The ratio between λ_opt；

2) by λ=λ_optSubstitution formula (2) acquires the transmission ratio M=λ of the gear-box after optimization_optN；

3) by λ=λ_optSubstitution formula (3) acquires the number of pole-pairs n of the double feed wind power generator after optimization_pM=n_pN/λ_opt。